Helicobacter pylori causes an inflammatory infiltrate in gastric mucosa that in about 10% of cases progresses to peptic ulcer disease or gastric cancer. Disease results from an interaction between strain-specific bacterial virulence genes and the particular host response, neither of which is well understood. Since experimental inoculation of rhesus macaques with H. pylori causes gastritis that closely mimics human infection, this model provides a unique opportunity to further our understanding of H. pylori pathogenesis. Rapid progress in genomics and gene expression technologies makes it possible to use the macaque model to study the H. pylori host-pathogen interaction by in vivo analysis of gene expression. We propose to extend our work in the rhesus model of H. pylori into an analysis of bacterial (Specific Aim 1) and host (Specific Aim 2) gene expression during experimental infection. Monkeys will be inoculated with a wild type H. pylori strain that reproducibly infects macaques, or with an isogenic mutant deleted in a specific gene implicated in H. pylori pathogenesis. Since pH is fundamental to host gastric physiology and to the niche in which H. pylori thrives, bacterial and host gene expression will also be examined after pharmacological manipulation of gastric pH. Quantitative real-time RT-PCR will be used to examine expression of H. pylori gene families that are likely involved in H. pylori-related disease or immune evasion. Gene expression in bacterial cells grown in vitro will be compared to that in cells isolated directly from infected monkeys. DNA microarray analysis will be used to study host expression of genes thought to be important in the fundamental processes of inflammation, proliferation, apoptosis, and cell signaling. Since the host immune response is increasingly recognized as a critical variable in the outcome of infection, we will also study host gene transcription after immunization with urease coupled with either CpG or alum adjuvant, in order to promote aTh1 or Th2 immune response, respectively (Specific Aim 3). These studies will provide a functional genomic understanding of the H. pylori host-pathogen relationship that may have implications for novel treatment or vaccine strategies.